1. Field of the Invention
The present invention relates to a method for controlling a compression ignition internal combustion engine.
2. Description of the Related Art
In recent years, in order to reduce a fuel efficiency and discharge of an internal combustion engine, a compression ignition internal combustion engine represented by a homogeneous-charged compression ignition internal combustion engine has been studied. However, the above described compression ignition internal combustion engine has difficulty in controlling the timing of ignition, in contrast to a spark ignition type internal combustion engine. In addition, the above described compression ignition internal combustion engine tends to cause knocking when a demand load of the engine is increased in case where fuel with high ignitability is used, and tends to cause flame off when a demand of the engine is decreased in case where fuel with low ignitability is used.
In order to solve the above described problem, a technology has been conventionally known which provides a fuel with high ignitability and another fuel with low ignitability, mixes the fuels, and supplies the mixture to the above described compression ignition internal combustion engine (see, for instance, Japanese Patent Laid-Open No. 2001-355471). According to the above described technology, the compression ignition internal combustion engine can be stably operated in a wide range of demand load, by adjusting a mixing ratio of the fuels depending on the demand load thereof. However, the above described technology requires the internal combustion engine system to comprise a plurality of tanks for separately accommodating each of the fuels with high ignitability and low ignitability.
In contrast, a technology has been known which uses a single fuel, and a part of the fuel is partially oxidized to produce an ignition inhibitor when the demand load of the compression ignition internal combustion engine is increased (see, for instance, Japanese Patent Laid-Open No. 2000-213444). In the above described technology, specifically, a part of a hydrocarbon-based fuel such as gas oil is partially oxidized to produce an ignition inhibitor such as formaldehyde, and has an advantage that only one fuel tank is required in the internal combustion engine.
However, this technology has an inconvenience of requiring a long period of time and a high temperature for a reaction of partially oxidizing the above described hydro carbon such as gas oil to produce formaldehyde.